Updatable Buffer Concept

An UpdatableBuffer is a special type of Buffer that provides an update operation for when the Buffer's ordering policy changes.

For a type to model the UpdatableBuffer concept it must have the following members.

Member	Where Defined	Description
`value_type`	Buffer	The type of object stored in the Buffer. The value type must be Assignable.
`size_type`	Buffer	An unsigned integral type for representing the number of objects in the Buffer.
`void update(const T& t)`	`UpdatableBuffer`	Revalidates this Updatable Buffer. An Updatable Buffer is invalidated if its ordering policy changes with respect to `t` but its internal structure does not reflect that change. Precondition: `t` is in the buffer.
`void push(const T& t)`	Buffer	Inserts `t` into the Buffer. `size()` will be incremented by one.
`void pop()`	Buffer	Removes an object from the Buffer. `size()` will be decremented by one. Precondition: `empty()` is `false`.
`T& top()`	Buffer	Returns a mutable reference to some object in the Buffer. Precondition: `empty()` is `false`.
`const T& top() const`	Buffer	Returns a const reference to some object in the Buffer. Precondition: `empty()` is `false`.
`void size() const`	Buffer	Returns the number of objects in the Buffer. Invariant: `size() >= 0`.
`bool empty() const`	Buffer	Equivalent to `b.size() == 0`.

push(), pop(), size(), and update() must be at most linear time complexity in the size of the Generalized Queue.
top() and empty() must be amortized constant time.

Use, modification, and distribution are subject to the Boost Software License, Version 1.0 at http://www.boost.org/LICENSE_1_0.txt